Conventional lift systems for the rotor assembly of flywheel energy storage systems (FESS) typically use the attractive force of permanent magnets in combination with an active control loop on an electromagnet to provide rotor assembly lifting force. Typically, permanent magnets are structured and arranged on the FESS so that attractive force between the permanent magnets lifts a portion, typically a substantial portion, of the weight of the rotor assembly. An electromagnet can provide the remainder of or, alternatively, all of, the force needed to completely lift the rotor assembly so that it can be rotated frictionlessly. Conventional lift systems also include bearings such as ball bearings to provide radial damping and limited axial stiffness.
The electromagnet and related control loop, however, are expensive and complex. The electromagnet also generates heat energy that is difficult to dissipate from the FESS because the electromagnets are contained within a housing under vacuum. In addition, the permanent magnets are generally located in regions of the FESS where the magnetic flux field can influence or affect the ball bearings, for example, due to magnetic flux leakage.
Thus, it would be desirable to provide new rotor assembly lift systems whereby the rotor assembly can be lifted without the use of an electromagnet and, further, to provide methods for passively-repulsively lifting the rotor. It would be particularly desirable to provide such systems and methods that would passively-repulsively lift a rotor assembly, for example, using permanent magnets that are structured and arranged so that the magnetic flux fields produced by each of the permanent magnets are of the same pole to produce a repulsive force between the permanent magnets. Moreover, it would be desirable to provide such systems and methods that include a mechanism for imposing a radial force of sufficient direction and magnitude to oppose the radial component of the repulsive force generated by the permanent magnets. It also would be particularly desirable to control the magnetic fluxes being generated by these permanent magnets in such a manner that they should not have an influence on ball bearings. Further, it would be desirable to provide rotor lift systems that would be less complex and less costly as compared to prior art lift systems, particularly those employing electromagnets and control loops.